Plasmids from tumorigenic mutants of Agrobacterium tumefaciens induced by NTG mutagenesis will be characterized physically by restriction endonuclease analysis. The site of the mutation in these avirulent strains will be determined by transformation of cured A. tumefaciens strains using plasmid DNA isolated from the mutants. The R factor directed chromosomal gene transfer in A. tumefaciens will be characterized and improved. Hfr donor strains will be isolated and used to map the A. tumefaciens chromosome by interrupted mating techniques. An attempt will be made to isolate strains carrying R'-type plasmids so that genetic complementation and cis-trans testing can be started. Work will continue analysis of the role played by cryptic plasmids in A. tumefaciens on host range. Transposons coding for antibiotic resistance phenotypes will be introduced into the cryptic plasmid supplying selectable markers so that genetic analysis can be facilitated.